Pool-independent labelling of synaptic vesicle exocytosis with single vesicle resolution in rat hippocampal neurons

Examination of synaptic vesicle recycling using FM dyes during evoked, spontaneous, and miniature synaptic activities

Synaptic vesicles in functional nerve terminals undergo exocytosis and endocytosis. This synaptic vesicle recycling can be effectively analyzed using styryl FM dyes, which reveal membrane turnover. Conventional protocols for the use of FM dyes were designed for analyzing neurons following stimulated (evoked) synaptic activity. Recently, protocols have become available for analyzing the FM signals that accompany weaker synaptic activities, such as spontaneous or miniature synaptic events. Analysis of these small changes in FM signals requires that the imaging system is sufficiently sensitive to detect small changes in intensity, yet that artifactual changes of large amplitude are suppressed. Here we describe a protocol that can be applied to evoked, spontaneous, and miniature synaptic activities, and use cultured hippocampal neurons as an example. This protocol also incorporates a means of assessing the rate of photobleaching of FM dyes, as this is a significant source of artifacts when imaging small changes in intensity.

The pH probe CypHer™5E is effectively quenched by FM dyes

Concurrent imaging of spectrally distinct fluorescence probes has become an important method for live-cell microscopy experiments in many biological disciplines. The technique enables the identification of a multitude of causal relationships. However, interactions between fluorescent dyes beyond an obvious overlap of their fluorescent spectra are often neglected. Here we present the effects of the well-established fluorescent dyes FM®2-10 or FM®1-43 on the recently introduced pH-dependent probe CypHer™5E. Spectrophotometry as well as live-cell fluorescence microscopy revealed that both FM dyes are effective quenchers of CypHer™5E. Control experiments indicated that this effect is reversible and not due to bleaching. We conclude that, in general, parallel measurements of both dyes are possible, with low FM dye concentrations. Nevertheless, our results implicate that special care has to be taken in such dual colour experiments especially when analysing dynamic CypHer™5E signals in live-cell microscopy.

Acid-sensing ion channels contribute to the increase in vesicular release from SH-SY5Y cells stimulated by extracellular protons

Acid-sensing ion channels (ASICs) have been reported to play a role in the neuronal dopamine pathway, but the exact role in neurotransmitter release remains elusive. Human neuroblastoma SH-SY5Y is a dopaminergic neuronal cell line, which can release monoamine neurotransmitters. In this study, the expression of ASICs was identified in SH-SY5Y cells to further explore the role of ASICs in vesicular release stimulated by acid. We gathered evidence that ASICs could be detected in SH-SY5Y cells. In whole cell patch-clamp recording, a rapid decrease in extracellular pH evoked inward currents, which were reversibly inhibited by 100 μM amiloride. The currents were pH dependent, with a pH of half-maximal activation (pH(0.5)) of 6.01 ± 0.04. Furthermore, in calcium imaging and FM 1-43 dye labeling, it was shown that extracellular protons increased intracellular calcium levels and vesicular release in SH-SY5Y cells, which was attenuated by PcTx1 and amiloride. Interestingly, N-type calcium channel blockers inhibited the vesicular release induced by acidification. In conclusion, ASICs are functionally expressed in SH-SY5Y cells and involved in vesicular release stimulated by acidification. N-type calcium channels may be involved in the increase in vesicular release induced by acid. Our results provide a preliminary study on ASICs in SH-SY5Y cells and neurotransmitter release, which helps to further investigate the relationship between ASICs and dopaminergic neurons.